The XB-70 Valkyrie was the prototype version of the planned B-70 nuclear-armed strategic bomber for the United States Air Force Strategic Air Command. Designed in the late 1950s, the six-engined Valkyrie was capable of cruising for thousands of miles at Mach 3+ while flying at 70,000 feet (21,000 m).
At these speeds, it was expected that the B-70 would be almost immune to interceptor aircraft, the only effective weapon against bomber aircraft at the time. The bomber would spend only a few minutes over a particular radar station, flying out of its range before the controllers could position their fighters in a suitable location for an interception. High speed also made the aircraft difficult to see on radar displays and its high-altitude flight could not be matched by any contemporary Soviet fighter.